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Bio 167 Exam - 2004 key

Bio 167 Exam - 2004 key - Bio 167 Exam Fall 2002 Name...

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Bio 167 Exam Name: Francis Scott Key Fall 2002 Below are 9 questions, each worth the indicated number of points. Good Luck. 1) (5 points) Steroids are an example of a hydrophobic signal. What effect does the hydrophobic nature of steroids have on their signaling mechanism? Because they are hydrophobic, they can freely pass through the plasma membrane. Therefore, the receptors for steroids are cytoplasmic. They also require carrier proteins for transport in the bloodstream. 2) (9 points) Briefly define what the terms amplification, crosstalk, and divergence mean in terms of signaling pathways (feel free to include a diagram if it helps you explain). Amplification: The increase in signaling flux generated at a step in a pathway. Crosstalk: The influence of one signaling pathway on a second. Divergence: Two or more distinct outputs from a single signaling input. Crosstalk Divergence Amplification 1
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3) (18 points) You identify on new signal, BoSox, that is perceived on the surface kidney tissue culture cells. a) How would you go about determining the number of binding sites for BoSox that are present on these cells? How would you determine the affinity of these sites for BoSox? In your answer, draw a diagram of the hypothetical results. (Assume that there is a single receptor subtype and that you have radiolabeled BoSox). Add radiolabeled BoSox in increasing concentrations to kidney cells. Allow binding to come to equilibrium. Wash off unbound and count what remains bound to the cells. Determine non-specific binding by adding excess unlabeled BoSox in the binding assay. Subtract non- specific from total binding and plot results as a function of concentration of labeled BoSox. The curve will approach the total number of receptors at its maximum and at 50% binding one gets the Km, a measure of affinity. (One could also replot as a Schatchard, and determine the K D and receptor number) b) Upon application of BoSox, the kidneys cells rapidly begin to proliferate. You do an experiment in which you measure cell proliferation in response to two equal applications (i.e. same dose) of BoSox, and obtain the following results: Explain why the second peak is smaller than the first. In general, what are some mechanisms that could regulate this reduced second response? The second peak is smaller due to receptor desensitization. Four mechanisms that could regulate this are: 1) Agonist removal; 2) Receptor uncoupling;
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Bio 167 Exam - 2004 key - Bio 167 Exam Fall 2002 Name...

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